Controlling Red Spider Mites on Orchids and Houseplants

How to Control Red Spider Mites on Orchids and Indoor Plants

Spider mites are a serious pest of orchids, indeed they are a pest of a great many other plants too, but with the warm weather we’re experiencing in the UK, today I wanted to remind you about the importance of controlling spider mites on orchids and other indoor plants.

Spider mites thrive in hot, dry conditions.  In warm, arid environments, spider mites are able to reproduce rapidly.  Given hot, dry conditions, a spider mite egg can hatch in just a few days.  Without the humidity to slow a spider mite’s growth down, after hatching from its egg, a spider mite reaches sexually maturity in less than a week, and goes on to lay hundreds of eggs, during its lifetime.  Naturally each of these eggs can hatch and then mature into adult spider mites, that will then go on to lay eggs and produce hundreds more spider mites.  Until before you know it, you’ve got a fully fledged spider mite infestation on your hands!

If you’ve grow orchids or houseplants, or you maintain terrariums, vivariums, orchidariums, or any other form of indoor garden, do remember to take time to provide your plants with some extra misting in hot weather.  Extra misting will increase the humidity levels, making it harder for spider mites to thrive.

This Amesiella minor orchid is growing inside my White Orchid Trial Terrarium; this plant is showing the effects of spider mite damage on its leaves. There is some yellowing across the leaves, there are also a few pin prick sized darker areas appearing over the leaves. This is where the spider mites have damaged the cells within the leaf.

How spider mites feed and damage plants

Spider mites feed on plants using their specially adapted mouthparts to pierce through the plant’s leaves, damaging the plant cells inside.  Spider mites feast on the chloroplasts and chlorophyll inside the leaf, as they feed from the plant’s leaves.

Chlorophyll is the green pigment within leaves, it literally gives leaves their green colour.  It serves a vital purpose for plants – chlorophyll doesn’t just make plants look pretty, as well as giving leaves their colouring, chlorophyll plays a vital part in the process of photosynthesis.  Plants need chlorophyll for photosynthesis, they cannot generate energy without it.  Chlorophyll is present within the chloroplasts, inside the plant’s leaves.

An orchid leaf showing spider mite damage.

Plants that are suffering from an outbreak of spider mites have a diminished supply of chlorophyll, along with damaged plant cells, and missing chloroplasts.  So spider mite affected plants are prevented, or limited to varying degrees, in their ability to conduct the process of photosynthesis, leaving plants without the energy they require for healthy growth.

Spider mites weaken plants, making their host plants less resilient and more susceptible to other pests and diseases.  If your plants are suffering with spider mites, make sure that you provide adequate waterings and fertiliser, applied at the advised dose, to strengthen your plants.  Spider mites can, in severe cases, weaken a plant so severely that the plant dies.

Types of spider mite that affect orchids

There are many types of spider mites: red spider mites and two spotted spider mites (both the same creature, which are known by their scientific name of Tetranychus urticae), flat mites or false spider mites (both the same creature, which are known by their scientific name of Brevipalpus californicus), orchid mites (also known by their scientific name of Tenuipalpus orchidarum) and Phalaenopsis mites (Tenuipalpus pacificus – which also feeds on other orchids and some ferns).  There are a great many other mites as well, including predatory mites, that feed on other creatures, rather than on plants.

The darker areas on this orchid leaf show older spider mite damage.

Spotting spider mites on orchids

Spider mites are very tiny, they measure one millimetre long or less.  Due to their minuscule size, they are not easy to spot, so often by the time you realise you have spider mites, you may well have a large infestation.  Even if you do identify your spider mite problem quickly, spider mites are voracious feeders, which given hot, dry conditions increase rapidly, and so a small number of these pests increase to be a large infestation, in just a short space of time.

I have often found that it was far easier for me to spot spider mite damage in a photograph, rather than in natural daylight.  If you’re looking for spider mites, I’d recommend taking close up photographs of your plants.  I’d advise you to take a number of photographs of the same leaf, flower, or stem.

In some of my extreme close up photographs, I can see a few tiny specks on my plants’ leaves, stems, or flowers, when I zoomed in.  Although the real giveaway is when the specks moved when I flick from one photograph to another!  Naturally there are countless different species of mites; not all mites damage plants.  For example, there are various species of Oribatid mites, which are found in almost every plant habitats, including in the soil, among mosses, and in leaf litter.  Oribatid mites feed on decaying plant matter, algae, mould, soil microflora, bacteria, and plant materials.

If you take a series of photographs of an orchid flower or leaf, it can help you to spot any creatures moving around and will help you to identify any pests.

We often refer to spider mites as red spider mites, but this can be misleading, as spider mites come in a range of colours.  Spider mites may be yellow, or greenish in colour, you might see brown or dark reddish brown spider mites, as well as the more famous red ones.  Spider mites can change colour at different times of year.

Spider mites can be found on any part of a plant, but they are often fond of inhabiting the underside of a leaf, where they enjoy some level of protection.  Spider mites often spin webs, to further protect themselves.

It’s not always easy to spot the effects of spider mites, as there may be only a gradual change in your plants’ appearance, as you see your orchids and houseplants every day.  Problems with spider mites can creep up, catching you unawares.

Take a closer look at this Amesiella minor specimen’s leaf, here you can see damage caused by spider mites. The brown markings you can see are older spider mite damage, showing where the spider mites have fed on this leaf. The spider mite uses its sharp mouthpiece to puncture the leaf, the mite is then able to suck out the contents of the leaf – including the cells, chlorophyll, and chloroplasts, using these for nourishment. The plant leaf cells that have been fed on by the spider mite have either been sucked out so are missing or they have been damaged, these areas appear as lime green or yellow at first. Chlorophyll and chloroplasts are necessary for photosynthesis. A diminished supply of chlorophyll and chloroplasts render the leaf less able to photosynthesise as effectively. Over time these light green areas turn brown. So the lighter areas that you see are more recently damaged and the brown areas are older spider mite damage. As pictured on the 13th March 2018, inside my White Orchid Trial BiOrbAir Terrarium.

Over time, the leaf damage caused by spider mites, which may initially appear as yellow or silvery coloured patches on the orchid’s leaves, may turn brown.  Although the leaves of spider mite affected plants often fall prematurely, before any further change in colouration occurs.  Leaves with a mottled or lightened appearance are often giveaway signs that spider mites are present.

This orchid leaf is showing the effects of spider mite damage. The darker areas show older spider mite damage and the silvery areas are where more recent spider mite damage has occurred.

Controlling spider mites on orchids and terrarium plants

Due to their quick rate of establishment and breeding, it’s important to act promptly when dealing with spider mites.  There are many methods of controlling spider mites:

Growing conditions

Firstly, by regularly misting water to increase the humidity levels, you make it harder for spider mites to establish themselves and to live successfully.  It’s much easier to maintain a humid environment inside a contained space, such as a glasshouse, a terrarium, vivarium, orchidarium, or bottle garden.  It’s harder to create a permanently humid environment on your window sill, or another open area, inside your home.

If you have Phalaenopsis plants, or other orchids, that you grow outside of a terrarium, I’d advise misting your plants with rainwater, reverse osmosis filtered water, or distilled water, regularly.  Place saucers or bowls of water around your plants – you could even make a beautiful feature by creating an indoor pond, aquascape, or water feature.  Or if you don’t want to increase the number of plants you care for, you could just have a bowl with floating candles, if you prefer.  Grouping plants together also raises the humidity levels around them, but by doing this you are also making it easier for any pests to spread to colonise all of your plants.

By raising the humidity levels and ensuring your plants enjoy optimum growing conditions, you will help your plants, but this alone will not control spider mites.  Thankfully, there are many actions you can take to actively control spider mites.

Spider mite populations can rapidly increase in size during hot, dry weather.

Actions

You can wipe over your leaves to manually remove spider mites.  For best results use small pieces of damp kitchen paper, use one tiny piece of kitchen paper per leaf, for maximum effect.  This action will help you avoid accidentally spreading the mites to other leaves or plants.  Don’t forget to wipe over the underside of your plant’s leaves and ensure you wipe over the plant’s stems.  Promptly remove, and bin or burn the used kitchen paper, after use.

You can wash spider mites off your plants, by taking your plants into the bathroom (it would be wise to remove any bathroom plants first, as a precaution!).  Tip your plants upside down and spray the plants with water, rinsing away from the plant.  There is absolutely no need to be harsh and to spray your plants with a powerful jet of water, just the action of the water running off the plants will be enough to dislodge at least some of the spider mites.

SB Plant Invigorator

I use SB Plant Invigorator on my orchids and indoor plants.  SB Plant Invigorator is a pesticide that’s biodegradable and non-toxic.  This organic treatment simultaneously provides plants with something of a foliar feed and the protection of a mildewcide, but its main use is to control aphids, mealybug, scale insects, whitefly, and spider mites.

Although SB Plant Invigorator is organic, I’ve never used this treatment outside, as I have no wish to harm any of the insects that are living in my garden, my Trials Area, or outside.  But I use SB Plant Invigorator on the orchids and plants that grow in terrariums and bottle gardens, inside my home.

I regularly spray SB Plant Invigorator on to my orchids and other indoor plants.  The best way to apply this treatment, is to remove all of the orchids from your terrarium, vivarium, or orchidarium.  Then, take the plants, one by one, and spray them with SB Plant Invigorator.  It naturally takes much longer to remove all the plants from each of your terrariums, but you will be applying a much more effective treatment if you use this method.

Don’t be tempted to leave a plant inside your terrarium.  You might think that one particular plant definitely doesn’t have any pests, but it’s wiser to spray all of your plants.  Leaving one, or more, plants inside your terrarium will reduce the effectiveness of your treatment.  You could spray SB Plant Invigorator onto the plants inside your terrarium, but this would not be anywhere near as effective a treatment as spraying the plants outside of their enclosure.

When you’re spraying your plants with SB Plant Invigorator: take one plant at a time, spray your plant from above.  Then turn your plant, first to one side, then to the other, going all around your plant to cover every stem and every leaf, as you spray.  Then turn your plant upside down and spray the underside of your plant and its leaves, too.

If you just spray your plant from above, it won’t take you as long to apply your treatment, but your will have left at least half of your plant unsprayed.  Pests are naturally drawn to the undersides of leaves, as this is safer territory.  You can often spot pests in the midst of congested groups of stems and leaves and in other hidden areas, so by rotating your plant and spraying each side, including the underside, you’ll maximise your chances of controlling the pests in your terrarium.

At times I also use biological controls to control spider mites and other pests inside my terrariums, I don’t use SB Plant Invigorator when I have biological controls inside my terrariums, as I don’t want to harm these beneficial insects.

Quarantine

When you look to introduce new plants to your collection, purchase plants from nurseries that you trust.  Inspect plants prior to purchase, if you can.  Purchase strong healthy looking plants and avoid any plants with silvery, or yellow, or brown coloured discolouration or markings on their leaves.

When you bring your new plants home, or when your new plants arrive in the post, wipe over your plants’ leaves with tiny pieces of damp kitchen paper, to remove any spider mites.  Do this thoroughly, wiping over both the underside and the topside of each leaf.  Use a new piece of kitchen paper for each leaf – just a tiny piece of kitchen paper will be sufficient for this job – so each sheet can be cut or torn into many pieces.

Place your new plants away from the rest of your plant collection.  Grow your new plants inside a quarantine terrarium, or in a separate room, inside your home.

Biological controls for spider mites

You don’t need to spray plants to control spider mites.  You could introduce the spider mites’ natural predators – predatory mites that feed on spider mites, to control the spider mites that live inside your terrariums or glasshouses.  This is easily done, you can order Phytoseiulus persimilis, the natural predator of spider mites, online.  I’ve ordered biological controls for spider mites, and other pests, many times.  Each time I’ve enjoyed a successful outcome – it’s something I’d recommend.

Spider mites affect a wide range of plants, including orchids. Outside in nature, plants benefit from the protection of predators, who feast upon spider mites and other plant pests. Whereas plants growing inside glasshouses or terrariums, or grown as houseplants inside our homes, do not usually have the benefit of these predators.
Phytoseiulus persimilis are the natural predator of red spider mites.

Spider mites in terrariums, vivariums, or orchidariums can be effectively controlled with Phytoseiulus persimilis, or with the predatory gall midge, Feltiella acarisuga.  An insect native to the UK, Feltiella acarisuga is a predatory midge whose larvae is very effective at controlling spider mites on outdoor field grown crops, outdoor plants, and greenhouse grown plants.

It is important to remember that predatory mites will, in most cases, be more susceptible to the effects of any pesticide or miticides than the spider mites themselves, as spider mites can develop a resistance to some of the treatments that were designed to control them.  So don’t be tempted to combine natural biological controls with insecticides, as you’ll wipe out the beneficial mites that you’ve paid for.

Other articles that may interest you………………..

To read the first part of my White Orchid Trial, please click here.

To see my Rainforest Terrarium being set up, please click here.

To see how my Orchidarium was created, please click here.

To read the first part of my Madagascar BiOrbAir Terrarium Trial, please click here.

To read the first part of my Miniature Orchid Trial, please click here.

To see a planting list of suitable plants to grow inside terrariums, bottle gardens, vivariums and orchidariums, please click here.

For house plant ideas, please click here.

To read about the new features of the 2017 BiOrbAir Terrarium, please click here.

To read about using decorative features inside your terrarium, please click here.

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